This invention relates to a modular waveguide assembly for a position measurement system, and, more specifically, in a preferred embodiment, to a mechanical modular waveguide assembly having an open channel for receiving and holding the waveguide, an integral tube fitted within the channel and having constrictions for locating the waveguide, a damping material which is injected into the channel and around at least a portion of the waveguide, a spool fitted within one end of the channel for holding a coil and the wires associated with the waveguide, and a flexible cable connector attached to pins on the spool for ease in connection to an electronics assembly.
A magnetostrictive linear position measurement system typically includes a magnetostrictive waveguide wire which is housed in a protective tubular housing about which a magnet is slidingly engaged. A current pulse can be sent through a wire near the waveguide, and this pulse interacts with a circular magnetic field of the magnet to induce a torsional strain wave in the magnetostrictive waveguide at the location of the magnet. The ability of a material to deform in the presence of a magnetic field is known as magnetostriction. The strain wave travels along the length of the waveguide and passes through a coil which converts the mechanical wave into an electrical signal. To obtain the location of the magnet, the time between the transmission of the current pulse and the reception of the signal from the coil can be measured and converted to a distance, because the speed at which the torsional wave will travel along the waveguide is known. Accordingly, when the magnet is connected to a movable mass, such as a liquid level quantity or a movable element in a machine tool for example, the exact position of the mass can be measured.
Damping elements can be secured to the end of the waveguide in order to prevent the strain wave from being reflected back along the waveguide and interfering with ongoing measurements. Typically, such damping elements have been provided in the form of round rubber discs which can be compressively arranged on the waveguide wire. Also, a sleeve can be provided for supporting and centering the waveguide. One such sleeve available from Balluff Inc. includes a plurality of rigid interlocking tubular pieces having a plurality of rubber rings inserted therein for centering the waveguide. In addition, an electronics module is typically connected to the coil for controlling the transmission of the current pulse and obtaining the position measurement by timing the signal received from the coil.
A number of disadvantages have been encountered with conventional magnetostrictive position sensors. For example, the assembly of such a sensor often requires a significant amount of manual labor such as, for example, the labor required in mounting and locating the damping discs onto the waveguide, or the labor required in fitting together the various pieces and rings of the support sleeve. In addition, conventional sensors have provided no separate mounting member for the entire waveguide assembly (which includes the pulse wire, damping elements, coil, and other components), such that this complete assembly could be handled and tested separately from the final product, and prior to being assembled with the electronics module and protective housing with which it will be used. In other words, heretofore no means was provided for handling, transporting, and stocking the waveguide assembly separate from the electronics module so that the waveguide assembly could be preassembled, pretested, and ready for connection to a customized electronics unit and housing assembly. In contrast, conventional sensors have required delicate handling of the components until the complete unit was constructed.
Moreover, no capability was previously provided for maintaining a number of preassembled waveguide assemblies and a number of preassembled electronic assemblies on hand, and then easily connecting any such waveguide assembly with any electronics assembly to be used upon demand by the customer. Furthermore, the delicate wires of the coil and the pulse wire were not conveniently held in one fixed location for simple and efficient interchangeability with the electronics unit.
U.S. Pat. No. 4,958,332, issued to Tellerman, discloses a damping device 30 for the remote end of a waveguide wire, which includes a tubular housing and a remote housing section 34. The remote end of the waveguide 22 is held within the damping device 30 by anchor 40 and the rest of the waveguide extends from the device. Spacers 46 and 47 are provided at the opposite ends of the chamber 45 of the device 30. The spacer 47 is preferably of a soft rubber to reduce front-end reflections. The chamber 45 of the device 30 is filled with a viscous liquid damping material. The waveguide 22, along with the damping device 30 which surrounds its remote end, fits within an outer protective tube 20 which connects to a housing 12 having a mode converter. A plug 14 provides an output indicating the spacing of the magnet 17 from the mode converter in the housing 12.
U.S. Pat. No. 5,545,984, issued to Gloden et al., discloses a waveguide 4 which is partially enclosed in a suspension sleeve 2. Damping element 6 is slipped over the waveguide 4 and is generally cylindrical in shape as is the suspension sleeve 2. The waveguide 4, suspension sleeve 2, and damping element 6 reside in an enclosure tube 3 which is mechanically supported at one end by a housing 17 through an end flange 19. A suitable mode converter (not shown) provides an electrical signal to an electronic circuit 26.
Generally, however, previously available magnetostrictive linear position sensors suffer from one or more of the above-mentioned problems, including difficulty in assembly, inability to easily handle and test the waveguide assembly separate from the electronics assembly and protective housing, inability to maintain a preassembled stock of waveguide assemblies which can be quickly and easily connected to a customized electronics assembly and support housing, and/or inability to quickly and easily connect any electronics assembly with a waveguide assembly of any length. Accordingly, an apparatus and method which avoids these problems would be desirable.
Accordingly, it is an object of the present invention to obviate the above-described problems.
It is another object of the present invention to provide a modular waveguide assembly which can be easily assembled.
Yet another object of the present invention is to provide a modular waveguide assembly which lends itself to automated assembly.
It is another object of the present invention to provide a modular waveguide assembly which can be preassembled, tested, and stocked separately from the electronics assembly, and housing with which it will eventually be used.
It is also an object of the present invention to provide a modular waveguide which can be preassembled, tested and inventoried, for later custom matching with a desired electronics assembly as needed for a particular application.
Another object of the invention is to provide a waveguide assembly which can be readily connected to a customized electronics unit and housing unit.
It is another object of the present invention to provide a waveguide assembly which can be quickly and easily connected to an electronics unit.
Yet another object of the invention is to provide a waveguide assembly which is relatively low in cost, requires relatively few pieces, and is relatively simple to assemble.
Additional objects and advantages of the invention will be set forth in part in the description that follows.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described above, there is provided a waveguide assembly for use in a position sensor having a protective outer housing to surround the waveguide assembly, a magnet mounted for movement along the protective housing, and an electronics module which receives an electrical signal from the waveguide assembly and provides an output representing the position of the magnet. The waveguide assembly can comprise an elongated channel, an elongated waveguide located at least partially within the channel, a conductor located at least partially within the channel, and a mode converter connected to the channel. The elongated channel has an opening extending along at least a portion of its length, and the mode converter is adapted to generate an electrical signal from a signal traveling along the waveguide.
Preferably, the mode converter of the waveguide assembly comprises a coil which is wound about a support element and has two ends which are secured at the support element. In this preferred embodiment, the support element is at least partially received within the channel and the waveguide is received within a bore in the support element. In another aspect of the invention, the support element comprises a base portion, a coil mounted to the base portion, and first, second, third, and fourth terminals connected to the base portion. The first terminal connects to a first end of the coil and the second terminal connects to a second end of the coil. Preferably, the base portion is in the form of a spool and includes a recessed portion about which the coil is wound.
It is also preferred that the waveguide assembly includes a support sleeve located at least partially within the channel and surrounding at least a portion of the waveguide. The support sleeve preferably includes constrictions spaced at irregular intervals along its length. In another aspect of the invention, the support sleeve comprises an elongated tubular member configured to receive a waveguide and having oppositely disposed openings at its ends. The tubular member can comprise an integral piece of flexible material, and a plurality of constrictions spaced along its length. The effective inner diameter of the tubular member is smaller at the constrictions than at the other portions of the member.
It is also preferred that the waveguide assembly includes a partially flowable material which is located within the channel in contact with a portion of the waveguide. Preferably, the damping material comprise a silicone material. In another aspect of the invention, a method of assembling the waveguide assembly is provided. A waveguide is inserted into a channel having an opening extending along a substantial portion of its length. A damping material is inserted into the opening and around at least a portion of the waveguide such that the damping material adheres to a portion of the waveguide. It is preferred that the damping material comprises an at least initially partially flowable material and that the damping material is cured after being inserted into the channel.
The waveguide assembly also preferably includes a gain unit connected to the channel and having at least one terminal adapted to connect to the electronics module. In another aspect of the invention, a pre-calibrated waveguide assembly is provided comprising a mounting member, a waveguide at least partially received within the mounting member, and a gain unit connected to the mounting member. The gain unit includes at least one terminal adapted to connect to the electronics module of a position sensor, and is selected according to the length of the waveguide to control the amplification of an electrical signal to be processed by the electronics module. Preferably, the gain unit comprises a resistor connected to a support element, and the mounting member comprises a channel to which the support element is mounted.
Still other aspects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration, of a best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other different aspects and embodiments without departing from the scope of the invention. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive in nature.